Ca+ entry through Cav2.1 (P/Q-type) channels initiates neurotransmitter release at most central synapses. Because small changes in intracellular Ca2+ can significantly alter synaptic efficacy, regulation of presynaptic Ca/v2.1 channels can powerfully influence processes of information transfer and storage in the brain. Ca/v2.1 channels undergo a feedback regulation by Ca2+ mediated by calmodulin (CaM) binding to the pore-forming alpha1-2.1 subunit of these channels. CaBP1 is representative of a family of neuronal Ca2+-binding proteins (NCBPs) that are related to CaM, but are expressed primarily in neurons. CaBP1 also binds to alpha1-2.1, but has surprisingly different effects than CaM in regulating Ca/v2.1 function. A splice variant of CaBP1, caldendrin, also associates with Cav2.1 channels both in transfected cells and in the brain. Therefore, presynaptic Ca2+ signals and synaptic strength may depend on the differential modulation of Cav2.1 by CaBP1, CaM, or other NCBPs. The goal of this application is to characterize the molecular mechanisms and neurobiological significance of Cav/2.1 modulation by CaBP1. Accomplishing this objective may resolve longstanding questions regarding the diversity of Ca/v2.1 channels in the brain, and suggest alternative therapeutic strategies for treating disorders linked to genetic defects in Cav2.1 such as familial hemiplegic migraine, spinocerebellar ataxia, and absence epilepsy. Molecular biology, immunochemistry, and electrophysiology will be used to address four specific aims: (1) to define the molecular determinants in alpha1-2.1 for binding to CaBP1 and CaM; (2) to determine how structural differences between CaBP1 and CaM affect interactions with Ca/v2.1; (3) to characterize the effect of CaBP1 on the pharmacological properties of Ca/v2.1; and (4) to compare Ca/v2.1 regulation by CaBP1 and caldendrin and co-localization of these proteins in the brain. These studies may reveal how other NCBPs could interact with target molecules thought to be regulated primarily by CaM, which may illuminate novel mechanisms controlling the development, plasticity, and ultimately, the behavioral output of the nervous system